Isoquercitrin is the 3-O-glucoside of quercetin and several unexpected bioactivities have been ascribed to it. For example, it has been reported that isoquercitrin can inhibit protein disulfide isomerase (PDI), an enzyme strongly implicated in thrombus formation. See Flaumenhaft et al., Arteriosclerosis, Thrombosis, and Vasc. Biol., 2015, 35:16-23. It is believed that inhibitors of PDI, e.g., isoquercitrin, can prevent or block thrombosis.
A Phase II/III clinical trial is ongoing to test the ability of isoquercitrin to inhibit is cancer-associated thrombosis. See the CAT IQ trial on the world wide web at clinicaltrials.gov. It is noteworthy that the daily doses of isoquercitrin administered in the trial are 500 mg and 1000 mg. These doses are unusually high, as compared to the doses of typical pharmaceuticals. It is likely that a large dose of isoquercitrin is required to achieve sufficient bioavailability, due to its relatively low oral absorption.
Enzymatically modified isoquercitrin (EMIQ) with higher water solubility has been developed to improve the bioavailability of isoquercitrin. See Murota et al., Arch. Biochem. Biophys., 2010, 501:91-97. Yet, EMIQ is a mixture of at least five bioactive isoquercitrin derivatives. See Akiyama et al., J. Food Hyg. Soc. Japan, 1999, 41:54-60. It is impractical to use such a mixture of active ingredients as a drug in humans according to present US Federal Drug Administration guidelines.
There is a need to develop pharmaceutical compositions with higher oral absorption of isoquercitrin via improved water solubility without the above-described drawbacks.